A recent trend towards a miniaturized semiconductor device structure in design criteria intensifies a demand for processing a material to be etched in a cross sectional shape of a high-density pattern. Currently, in a plasma etching apparatus for use in manufacturing a semiconductor device or a flat panel display (FPD), a generation of high-density plasma is indispensable for a miniaturization of a semiconductor device structure or a high-rate etching process for a substrate to be processed (a semiconductor wafer, a glass substrate or the like). Accordingly, in a parallel plate plasma etching apparatus, in order to generate the high-density plasma, various investigations or trials have been attempted by way of increasing a frequency of a plasma exciting radio frequency RF from a conventional standard frequency of 13.56 MHz to a remarkably high frequency (e.g., 40 MHz or higher).
Along with the high density of the plasma, a demand for uniformity of etching characteristics (especially, an etching rate, an etching pattern or the like) on a substrate becomes more and more strict. Conventionally, in the parallel plate plasma etching apparatus, an upper electrode serves as a shower head having a plurality of gas injection openings, and an etching gas is discharged through the shower head toward a substrate on a lower electrode. Further, a glow discharge occurs between the electrodes due to a radio frequency power applied thereto, thereby generating a plasma of the etching gas. As for the etching gas, there has been widely used a mixed gas wherein an etchant gas containing halogen atoms such as chlorine or fluorine is mixed with an inert gas, e.g., Ar, and/or an additive gas, e.g., O2.
However, in the conventional parallel plate plasma etching apparatus, it is difficult to realize uniform etching characteristics on a substrate to be processed and, further, it is hard to control etching characteristics, especially on a peripheral portion of the substrate. According to the finding of the inventors of the present invention, even if a flow rate of an etching gas to be introduced into a processing chamber or a pressure in the chamber is adjusted to be set at predetermined specific values, it is difficult to precisely control a flow or a density distribution of the etching gas in a space above a substrate, i.e., in a plasma generation region, and especially those in a vicinity of the peripheral portion of the substrate are likely to be nonuniform and incontrollable.